1. Field of the Invention
A tensioning apparatus for stretching screen fabric or other membrane.
2. Description of the Related Art
Serigraphy or silk screening is a process for producing an image on a working surface such as a sheet of paper with the aid of a stencil. The process involves stretching screen fabric on a frame and applying a stencil on the screen fabric conforming to the areas not to be colored in the final image. The screen fabric is laid adjacent the image receiving piece or substrate such as paper, metal, wood, plastic, masonry, cloth or bristol board and the desired pigment is applied across the screen fabric. The pigment penetrates those areas of the screen fabric not covered by the stencil to produce the desired image on the image receiving piece.
Various frames for stretching the screen material have included simple frames, roller frames, draw bar frames and expansion frames.
Numerous prior art methods include using a generally rigid wood frame and merely pulling the fabric over the frame and then fastening the fabric in place by tacks, staples or adhesive
Another prior art method has been to provide a frame member with wedge means adapted to be driven into each corner of the frame to create the tension on fabric material secured to the frame. This method does not permit effective further adjustment of the tension on the material after the tension has once been applied by the wedge means. In addition, it is difficult to control the initial tension on the material because of the inability to control the tension on each of the four corners of the frame equally.
Another prior art method has been to use a metallic type frame and secure fabric material thereto by means of a groove in the metallic frame. Tightening of the fabric material is accomplished by expanding each of the telescopically disposed corners creates the tension on the material.
Specific examples of such devices are found in a number of United States patents.
U.S. Pat. No. 4,430,815 shows a fabric tension apparatus for screen printing frames wherein the edge portions of a screen fabric are attached to a screen printing frame. The frame has discrete springs in contact with the fabric. The springs provide limited movement of the fabric toward a substrate by deformation of the springs instead of relying only on stretching of the fabric.
U.S. Pat. No. 3,601,912 teaches a frame for supporting and stretching a rectangular printing screen comprising a plurality of frame members connected by and journaled within corner members. The frame members have means for gripping the screen material along each edge and are rotatable within the corner members to apply tension to the screen to create the desired tension.
U.S. Pat. No. 4,525,909 discloses a screen tensioning and printing frame including sets of parallel rollers coupled to corner members. Each roller has a longitudinally extending peripheral fabric locking groove defined in part by straight surfaces. Adjacent and on opposite sides of the locking groove is at least one fabric registration groove on the periphery of each roller.
U.S. Pat. No. 3,908,293 shows a screen tension and printing frame including sets of parallel rollers wherein each roller is coupled to an edge portion of a screen. The screen is in sealing contact with a dam member located inwardly of the rollers. Each roller is provided with means to facilitate selective rotation and locking of each roller in a position so that a desired tension may be applied to the screen.
U.S. Pat. No. 4,409,749 teaches a stretch frame for sheet material such as printing screen utilizing tensioning rollers to be secured to the sheet edges and then rotated to stretch the sheet material. The rollers may be rotatably received within laterally opening channels in the frame and restrained against reverse rotation to release the sheet tension by a ratchet device extending along a substantial length of each roller.
U.S. Pat. No. 3,482,343 discloses a stretch frame for stressing sheet material such as printing screen. In mutually perpendicular edgewise directions, the frame includes frame members and floating bars for attachment to the edges of the sheet material to be stressed, and means independently adjusting the frame members and floating bars to stretch the sheet material in the edgewise direction in such a way as to permit both coarse and fine adjustments of the sheet tension.
U.S. Pat. No. 3,924,343 teaches a frame for stretching material secured thereto comprising elongated defining frame elements having mitered ends adapted for juxtapositioning with the confronting end of an adjacent frame element with rotatable stud means coacting between adjacent frame elements coupling the latter together and providing for movement of the coupled frame elements relative to one another upon rotation of the stud means to stretch the material attached to the frame.
U.S. Pat. No. 3,485,165 shows a silk screening frame having longitudinal and transverse frame members defining a central well with a silk screen stretched across the bottom of the well and through which pigment may be pressed to form a given design. Each frame member has a slide guided thereby for movement toward and away relative to the well. Each slide includes a groove for receiving the adjacent marginal edge the screen formed with converging fingers into which an anchor pin is inserted to hold the screen to the guide. The slides are guided relative to their respective frame members so that the slides are prevented from twisting out of alignment.
U.S. Pat. No. 4,442,772 discloses a stencil frame enclosed tightly by a pneumatically operated frame. Once the stencil frame is enclosed, the pneumatic tensioning frame is inflated pulling a screen fabric outwardly to stretch the screen fabric with movement of the frame members and frame supporting portion of the tensioning frame so that the top wall of the frame member is pushed tightly and intimately against the underside of the screen fabric.
U.S. Pat. No. 3,541,957 teaches a stretcher device enclosed tightly by a pneumatically operated frame. The stencil screen is secured on all sides by the movable portions of the surrounding pneumatic tensioning frame. The pneumatic tensioning frame is then inflated uniformly with compressed air and extended to cause the screen to be tensioned uniformly in all directions. The screen is then tacked or stapled or otherwise fastened to the stencil frame. The pneumatic frame comprises a plurality of pneumatically operated frame members having a fixed member engageable with the stencil frame and a movable member on which the stencil screen is secured for movement under penumatic pressure. The pneumatic frame members are provided with connection means for assembling the individual frame members end to end or at right angles to provide a rectangular frame enclosure of any desired size in which the movable frame member is adapted to move under pneumatic pressure to tension a screen stencil in all directions uniformly and continuously around the periphery of the stencil frame.
U.S. Pat. No. 3,991,677 discloses a printing screen and tensioning means including a rigid frame structure formed of channel shaped side members joined at the corners of the frame structure. The underside of each frame member receives a parallelogram structure having a first and second side member connected by pivot links. The first side member is disposed adjacent the inner margin of the frame member and longitudinally movable by a screw drive; while, the second side member is guided for transverse movement in the frame member to and from the first member and having continuous screen attachment means. The printing screen includes a continuous clip element at each side received on the attachment means whereby upon operation of the screw drives the second side member applying a laterally outward force for uniformly stretching a corresponding side of the printing screen.
U.S. Pat. No. 4,451,997 shows an embroidery hoop style stretcher frame for stretching and holding fabric during stitching and/or painting. The stretcher frame includes a first frame member with an outer rectangular U-channel portion and a second frame member having an inner rectangular U-channel portion which fits matingly within the outer U-channel portion of the first frame member so that fabric may be sandwiched between the inner and outer U-channel portions.
U.S. Pat. No. 4,860,467 teaches a method of tensioning screening material on a tension frame for use in a silk screen process including the steps of squaring the material, attaching the material to rotatable frame members along a portion of their length by adhesive, rotating the frame members until the appropriate tension is reached and securing the frame members in position. The fabric may be retensioned without removal. The frame includes four rotatable cylindrical elements including a plug at each end which has a plurality of radial bores for rotation by a spanner wrench.
U.S. Pat. No. 3,422,554 shows a frame for stretching screen for use in serigraphic processes. The frame comprises a plurality of support members defining a periphery. Clamp means comprising a first and a second clamp member and a securing means therebetween is attached to at least one of the support members by an adjustment means. The screen to be stretched is placed within the periphery defined by the support members and sandwiched between the securing means and the clamp members. An opposite margin of the screen is secured to an opposite support member and the adjustment means is operated to provide adjustment of the position of the assembled clamp means thereby providing adjustment for the tension in the screen.
U.S. Pat. No. 4,462,174 discloses a process and apparatus for prestretching screen fabric usable in screen printing. The screen fabric is tensioned using a tensioning device and subsequently an alternating load is applied to the screen fabric to prestretch the screen fabric. The loading may be applied along a direction parallel to, perpendicular to, or at an intermediate angle to the plane of the screen fabric.
U.S. Pat. No. 3,391,635 shows a silk screen printing apparatus having clamping means for uniformly and tightly stretching the screen over a frame by exerting a balancing pushing force on the screen while pulling on the screen with a plurality of hydraulic cylinders arranged around the frame.
Additional examples as shown in U.S. Pat. No. 3,176,843, U.S. Pat. No. 4,373,441 and U.S. Pat. No. 4,430,814.